1. Field of the Invention
The present invention relates to the steering of optical beams and more particularly to the steering thereof without the need for mechanical gimbals.
2. Description of the Related Art
Present methods for steering optical beams in laser radar of laser communication systems utilize mechanical gimbals to point a telescope assembly or a mirror in the appropriate direction for beam transmission or reception. Recent developments in liquid crystal optical phase shifting devices enable electronic steering of coherent optical beams. However, these devices permit steering only over small angles (approximately four degrees, one dimension) with efficiencies exceeding 50 percent. Since coverage angles in excess of 90 degrees in two dimensions are typically needed for laser communication and laser radar systems, these devices alone are insufficient in themselves to build a complex system without gimbals.
The article entitled Optical Phased Array Technology, Proceedings of the IEEE. VOL. 84, NO. 2, February 1996, pages 268-298, discloses an optical phased array beam steerer suitable for small angle beam steering. Section II, Overview of Liquid Crystal Optical Phased Array Concepts, shows that with current liquid crystal materials high efficiencies can only be achieved for small steering angles. As a specific example, a phased array with center-to-center spacing of 2 μm, a liquid crystal layer thickness of 5 μm, and operating at a wavelength of 1.55 μm will have an efficiency greater than 50% only for steering angles less than 5 degrees, based on the equations presented in this reference.